|“Biker’s nodule”- perineal nodular induration of the cyclist
The “biker’s nodule” is a rarely appearing perineal nodular induration of the cyclist. Repeated microtrauma to the subcutaneous fatty tissue or collageneous tissue, caused by pressure or vibration which the bicycle’s saddle exerts on the perineal region, leads to collagenous degeneration, myxoid alteration and pseudocyst formation. Because of the painful subcutaneous nodules the patient is often forced to reduce or even give up his training. Therapy of the “biker’s nodule” consists in avoiding the pathogenetic factors, i.e. giving up training for a temporary period of time and reducing pressure on the perineal region. Intralesional injection of either hyaluronidase or corticosteroids may also be helpful.
Perineal nodular induration (“Biker’s nodule”)
Perineal nodular induration (PNI) is a fibroblastic pseudotumor that presents almost exclusively in male cyclists. It develops in the soft tissues of the perineum immediately posterior to the scrotum, as a bilateral or single, central or lateralized mass. Although well known to sport medicine specialists, it is a scarcely documented entity in the pathology literature. We present 2 cases of PNI with fine-needle aspiration cytology and immunohistochemistry. They consisted of a paucicellular fibroblastic proliferation containing CD34-reactive spindle and epithelioid cells, small foci of fibrinoid degeneration, numerous blood vessels, and entrapped groups of mature fat cells. Our cases show that the histopathological features of PNI are more varied than those previously described and its immunohistochemical profile is wider. A central cystic focus and a zonal pattern are not consistent features of this entity. The lesional cells can express CD34, a hitherto unreported immunohistochemical finding.
|Perineal nodular swelling in a recreational cyclist
The diagnosis of a biker’s nodule was made, based merely on the clinical history, the typical location and the imaging findings.
The size of the lesion rarely exceeds 3 cm. Symptoms include pain on pressure and when sitting on the saddle, which often forces the athlete to give up riding the bicycle. On palpation, the nodule is solid and sometimes adherent to the adjacent soft tissue. The lesion is believed to result from increased pressure, vibration and friction between the ischial tuberosities and the hard saddle, characteristic of racing cycles or mountain bikes, with constant rubbing of the superficial perineal fascia against the bony structures.
Histopathology shows a myxoid degeneration of the fatty tissue and collagen fibers overlying the ischial tuberosities, caused by necrosis of the superficial perineal fascia, sometimes with formation of pseudocysts. The lesion is not well vascularized. Imaging characteristics are only rarely reported. Ultrasound shows a hypo-echoic nodule, with absence of any increased power Doppler signal. Small internal cystic areas may be seen as well. On computed tomography (CT), the lesion shows no uptake of contrast agent, which is explained by the hypovascular nature on histology. To our knowledge, magnetic resonance imaging (MRI) has not been reported. As in CT, there is no uptake of contrast medium.
The primary role of imaging is to determine the exact extent of the lesion. Ultrasound and MRI are particularly helpful in locating the lesion in the subcutaneous fatty tissue and close to the ischial tuberosities. In most clinical scenarios, ultrasound will suffice for imaging evaluation. Imaging has an additional role in the differentiation between ‘biker’s nodule’ and other causes of a perineal swelling. The differential diagnosis includes abscess, epidermal cyst, (cutaneous) adnexial mass, lipoma, and malignant tumor (soft tissue sarcoma or metastasis).
In biker’s nodules, signs of inflammation or abscess formation are lacking, and the absence of contrast agent enhancement on MRI excludes malignancy. The primary therapy consists of avoidance of the causative factor. Rest alone is generally not sufficient as therapy. The condition almost systematically imposes saddle adjustments or change (different saddle shape and coverings in order to improve individual saddle fitting). Special attention should also be given to the pants of the cyclist. If the lesion is therapy resistant, some authors recommend local injection of corticosteroids or hyaluronidase. If none of these therapies is efficacious, surgery can be considered.
A high index of suspicion is required for diagnosis, and, therefore, clinical history is the most important clue to the correct diagnosis. When a soft tissue nodule in the perineal region is seen in a cyclist, both the clinician and the radiologist should consider the diagnosis of a ‘biker’s nodule’.